Terumos 2:6-3:1

One may take terumah from olives that are suitable for oil (i.e., of superior quality) for olives that are to be pickled, but not vice versa. One may take terumah from unboiled wine for boiled wine (mevushal) but not vice versa. The general rule is that if two types cannot be planted together because of the prohibition against mixed species, then one may not take terumah from one for the other, not even from the better kind for the lesser kind. If they may be planted together, one may take terumah from the better kind for the lesser kind but not vice versa. If one did take from the lesser for the better, it is valid terumah except in the case where one took terumah for wheat from darnel (a weed sometimes called “false wheat”). This is because darnel is not fit for human consumption. Cucumber and muskmelons count as one type; Rabbi Yehuda says they are two types.

Terumos 3:1

If one took a cucumber for terumah and it turned out to be bitter (and therefore questionable for human consumption), or if he took a melon and it turned out to be rotten, what he took is terumah and must be treated as such but he must also take terumah again. If he took a barrel of wine as terumah and found it had turned to vinegar, if it turned before he took it, it is not terumah; after, it is. If he doesn’t know, it is terumah and must be treated as such but he must also take terumah again. If the first terumah mixes with chulin (non-sanctified food), it does not render it meduma (which may not be eaten by a non-kohein), nor must a non-kohein who eats the first terumah repay an extra fifth. The same is true with the second terumah.